The Great (Ape) Taxonomy Debate

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Cadell Last is an evolutionary anthropologist (MSc.) with a background studying chimpanzee sleeping patterns and the emergence of human bipedalism. He is currently working on an animated science channel with PBS Digital Studios and merging anthropological and cybernetic theory with the Global Brain Institute. Follow on Twitter @cadelllast.

As an undergraduate studying primatology, I was always confused about great ape and human taxonomy. Were we great apes? Or were we hominids? Or were we both? What was the consensus and was there logical and scientific reasons for lumping or splitting? To be completely honest, I never really resolved this internal dilemma. In hindsight it seems ridiculous considering how much time I spent thinking about it.

However, as an evolutionary anthropologist I have been asked whether I consider humans to be great apes. I always confidently reply that we are. Upon reflection I think I have responded this way because of my early evolutionary science influences. In college I read a lot of Richard Dawkins and Jared Diamond. Both of these academics have popularized the notion that we are the “fifth ape” or the “third chimpanzee.” (Diamond, 1992; Dawkins, 2004). In fact, Wikipedia and modern taxonomic classification both support this claim:

So it seems to be an open and shut case right? Why should I lose any sleep over this taxonomic grouping? Humans are great apes.

However, I don’t think it is this straightforward. Whether we are great apes (lumping) or aren’t great apes (splitting) doesn’t just affect research and theory, but it also affects how we conceptualize what it means to be human. So what is the scientific evidence and reason behind lumping us in with the great apes?

The main justification for grouping humans and great apes together is anatomical and morphological. We share the same ‘Y5’ pattern (five cusps or raised bumps arranged in a Y-shape), a rotating shoulder, no tail, posteriorly positioned scapula, fused caudal vertebrae, and a large and complex brain (Marks, 2009).

To me, the most important of these anatomical and morphological similarities is the “large and complex brain.” It is true that the great apes have larger brain to body size ratios than all other primates. And it is this large brain size that allows the great apes to accomplish incredible intellectual accomplishments both in the wild and in laboratory settings. However, the human brain is at least three times the size of any great ape brain. The human brain exploded in size with the birth of the genus Homo, approximately 2 million years ago. Most importantly, the human brain has enabled levels of communication and intelligence unparalleled in the history of life on Earth.

This is no trivial difference. So why do we group ourselves with species that are quite different from ourselves? I think there are two main reasons: a) a scientific tradition that emphasizes ancestry over emergence and b) an evolutionary past that has left us with no extant sister taxa.

Biological anthropologist Jonathan Marks has recently explored the first of these reasons in great detail (e.g., Marks, 2009; Marks 2012). Marks claims that by lumping our species in with great apes, researchers create a human evolutionary framework that begins by assuming we never really became human. It also implicitly rejects an important Darwinian theoretical approach by focusing on descent, as opposed to divergence (Marks, 2009).

British anthropologist Robin Dunbar agrees with this basic philosophy, and stated this clearly in a 2008 article titled Why Humans Aren’t Just Great Apes. Within this article Dunbar claims that humans are different from great apes in one critical respect: our imagination (Dunbar, 2008). I would contend that there are several more critical differences between the human mind and the great ape mind, but I do agree with Dunbar’s approach of stressing the ways in which humans are divergent from the great apes.

The classification of humans as great apes is also dependent on a historical contingency: we have no extant sister taxa. In the not-so-distant past humans shared this planet with several other humans. In fact, the last non-sapiens member of the Homo line suffered extinction approximately 13,000 years ago. This means that for over 90% of our species existence, we shared Earth with other humans. Despite this, none remain today (and it is probably our fault). If one or more of these other humans had survived into contemporary times, our taxonomic classification scheme for humans and great apes would undoubtedly look much different. Instead of focusing on the similarities between humans and chimpanzees, or humans and gorillas, we would likely shift our attention to focusing on the similarities between humans and … other species of humans.

It would be difficult for taxonomists to lump two or more human species in with the great apes. The differences would be far too striking.

The implications of splitting humans from great apes taxonomically would be beneficial. Conceptually it would allow researchers to better understand the hominid/ape divergence and the key differences between humans and great apes today. But perhaps more importantly, splitting humans from the great apes allows us to reconceptualize our own humanity. We are not the great apes; we are humans. The great apes are our closest extant relatives, and it is incredibly important to study, protect, and conserve them. However, we can’t use their title as closest extant relatives as a strategic rhetorical device to emphasize similarity.

About the Author:Cadell Last is an evolutionary anthropologist (MSc.) with a background studying chimpanzee sleeping patterns and the emergence of human bipedalism. He is currently working on an animated science channel with PBS Digital Studios and merging anthropological and cybernetic theory with the Global Brain Institute. Follow on Twitter @cadelllast.

18 Comments

I’m afraid there is some confusion here about why humans are considered “Great Apes”, and also about some basic phylogenetic concepts.

First, “lumping” humans in with the other Great Apes is not an issue of morphology similarity. It is a phylogenetic question. Because humans are evolutionarily more closely related to chimpanzees/bonobos than either is to the other Great Apes, the category “Great Ape” would be paraphyletic if humans are excluded. This is a no-no from a cladistic classification standpoint. If the term “Great Apes” is to be evolutionarily meaningful, it must include humans.

This raises the second issue, which is the notion of what an “extant sister taxon” is. Again, this is not about morphological similarity, it is about evolutionary relatedness. A sister taxon is the closest living relative, that is the taxon with which another taxon shares its most recent common ancestor to the exclusion of other extant taxa. Humans do have an extant sister taxon, and it’s chimps/bonobos.

@TRGregory – your point is well taken. However, consider the following from Marks, J. (2012) (full citation above):

‘We were not always apes, we became apes as a consequence of the cultural privilege accorded to genetic data and approaches at the end of the 20th century. We became apes as a dialectical relationship of descent and modification became replaced by a reductive view, in which descent (which genetics reveals well) supersedes modification (which genetics does not reveal well).

The genetic apeness of people also meshed well with the phylogenetic focus of cladistics, and provided a useful tool with which to bludgeon the creationists; but its truth value is predicated on the acceptance of genetic relationships as transcendent and the suppression of ecological relationships. Whether you choose to see us, then, as genetic apes or as ecological ex-apes is not so much a scientific issue as an ideological one. Both identities are true. The question is: Which identity are you going to highlight?”

I personally believe in highlighting the difference at a morphological and behavioural level. On a cladistic tree we may be considered great apes but I think it is more useful for future primatological research to conceptualize the clear ecological divergence between our species and the great apes.

That being said, I will concede that I should have discussed phylogenetics in this paper. It was an oversight.

Were we great apes, or were we hominids – or were we both? We were both. And we still are.

As to the Dunbar article, it seems to me that one could just as well argue that humans are not just mammals, or not just vertebrates. It might be a little anthropocentric to make that case, but no matter – it’s true enough, as long as one recognizes that we are talking about different-than, and not separate-from.

Different-than and separate-from are two distinct ideas. If my grandmother were to consider her grandchildren, I am different than my other siblings and cousins, but genealogically I am not a separate group – I am still a grandchild. Altering the size of my brain, colour of my hair, number of toes, etc., would not change this. A redwood is still a tree, no matter how tall, raven is still a bird, no matter how smart, and bat is still a mammal, no matter its aerial talents. These taxonomic groupings are based on descent, not dimensions or merit.

Humans are most certainly different from chimpanzees and bonobos, gorillas, and orangutans. And in turn, each of those may claim to be different from all the others, unique in its own way. But great apes we all remain.

@cadelllast – with respect – your choice to focus on the ecological differences may indeed be a fine tool for your primatological research, but this is distinct from the taxonomy. As per the Marks 2012 citation, perhaps the piece would be better framed as an ecological debate (if this is an open question) or an ideological one.

You’re welcome to use the term “Great Apes” to refer to apes other than humans if you like. But it will be a paraphyletic grouping and not meaningful evolutionarily. We certainly still tend to do so with other paraphyletic groupings like “invertebrates”, “fishes”, and “reptiles”. In terms of common usage, there is no strict requirement for the groupings to be based on evolutionary relatedness. Marks seems to be upset about the use of genetic data versus morphology/ecology, but that’s not the point — if you want to base your taxonomy on evolution rather than, well, whatever other criteria you might like (at the risk of being very subjective about it), then you include humans among the Great Apes. It so happens that genetic data are better at revealing these phylogenetic relationships in many cases, precisely because morphology can change so much in individual lineages.

So, if you are not using an evolutionary criterion, then you can decide as you like if we’re “apes”. But then I don’t see the point of this article, to be frank.

It doesn’t help that you combine vernacular terms like “apes” with more technical taxonomic ones like “hominid” and “lumping vs splitting”. It’s not “splitting” to separate humans from other apes in a taxonomic sense, it’s just deciding that you’d like an informal term like “animals” to indicate species other than your own regardless of evolutionary relatedness. That is, unless you are wondering about “ape” as an actual taxonomic group, in which case you would need to justify a criterion other than evolutionary relationships if you decide to somehow combine other ape species to the exclusion of humans.

@TRGregory 1) The point of the article was that emphasizing similarity between great apes and humans emphasizes were ancestry, as opposed to our divergence. There are a number of important differences between humans and great apes that I feel get overlooked in primatology because of this. Also, my point with historical contingency has to do with the fact that our conceptualization of difference between ourselves and the great apse would be much different if one (or more) of our extinct hominid relatives had survived into contemporary times. My mistake in this article was to state “we have no extant sister taxa.” So my fault on that statement and thanks for pointing it out.

2) “That is, unless you are wondering about “ape” as an actual taxonomic group, in which case you would need to justify a criterion other than evolutionary relationships if you decide to somehow combine other ape species to the exclusion of humans.”

I think this exactly incapsulates what I would propose. The emergence of our species was such a unique event in the history of life that it makes little sense to continue grouping our species in with species that are ecologically and morphologically very distinct from ourselves.

I think this demonstrates the limitations of Taxonomy. There is certainly a human-centric bias to the way we classify things. For example we have 6 kingdoms; Animalia, Plantae, Fungi, Protista, Archaea, and Bacteria. That seems strange to me. It is like classifying sports as running, ball, hockey, baseball and football. Shouldn’t it be Eukaryotes, Archaea, and Bacteria. With Animalia, Plantae, Fungi, Protista being a layer below Eukaryotes? Because we see such a big difference between ourselves and plants and fungi we give ourselves a complete kingdom though it may not be deserved. Similarly, organisms that have much greater genetic differences from each other than that between sapiens and other great apes are often only differentiated at the species level whereas the perceived difference between chimps and humans seems to earn us a whole new genius. By that logic would not african and indian elephants have separate genii? So on the other end of the spectrum, some have suggested humans should be called pan sapian or chimps be called homo troglodytes. I get that we are different, but not so long ago if you were to ask someone if africans or orientals should be included as members of the homo sapien species you would have had the same argument about how Europeans are so much more intelligent and civilized that it would be offensive to god to suggest we are the same. And there is the difficultly, taxonomy, despite its best efforts still has some arbitrary aspects to it. Furthermore, nature once again resists our attempts to categorize it into discrete groups which does not reflect the true relationships between organisms. So how do you construct a phylogenetic tree for all organisms that is based only on measurable criteria?

I hardly know where to start, except to thank TR Gregory for vital corrections about contemporary taxonomy. Oddly, considering all the talk about lumping and splitting, I find no mention of the taxa homininae and hominini, which recognize the close relationship between humans and the African apes apart from the other so-called great apes. Finally, I’m concerned about the political implications of placing Homo sapiens on a taxonomic pedestal. This could be a godsend for a restoration of human biological imperialism and a death sentence for other surviving primates. If the evidence pointed inexorably to such a classification of humans, then that’s science and let the chips fall. However, this discussion demonstrates that it’s just one subjective viewpoint.

Re: “I would contend that there are several more critical differences between the human mind and the great ape mind, but I do agree with Dunbar’s approach of stressing the ways in which humans are divergent from the great apes.”

How does that statement square with the following?

“Nowhere is the weakness of the design argument more flagrant than when we compare men and apes. Creationists passionately insist that these species have separate ancestries. If so, why did the Intelligent Designer give us 98 percent of a chimpanzee’s or gorilla’s genes, and design only 2 percent of our genes anew?”

I thank drglennking and Bill_Crofut for raising the very important point of cultural perception and creating rather arbitrary support for creationist thinking. Personally, I view taxonomical classification as a rather arcane artifact of early attempts at scientific understanding than having any any real relevance to modern knowledge. However, in this case splitting man from beast might tip the balance of power towards the growing cultural influence of scientific ignorance.

Oh yeah, btw reading a little bit about how cladistics work wouldn’t hurt. We are animals. It does not matter how different you think we are from the next ape. That only makes you think the branch is longer, not that we don’t belong there. Also, other evolutionary anthropologists should be ashamed of such a big demonstration of not understanding the basic principles of phylogenetics and evolutionary studies, like ignoring the last, oh, 80 YEARS IN THE DEVELOPMENT OF EVOLUTIONARY THEORY. Yup, 1930s. Congratulations!

You aren’t alone in expressing doubt concerning classification in taxonomy; Prof. W. R. Thompson would seem to have had his doubts nearly 60 years ago:

“What we call the natural system of classification is a proof of evolution since it can only be explained as a result of evolution….The argument specifically implies that nothing is exempt from this evolutionary process. Therefore, the last thing we should expect on Darwinian principles is the persistence of a few common fundamental structural plans. Yet this is what we find…[T]here is often controversy and, uncertainty about the definitions of genera. species, and varieties; but taking the taxonomic system as a whole, it appears as an orderly arrangement of clear-cut entities which are clear cut because they are separated by gaps. These gaps Darwin explained by the hypothesis that the intermediates are constantly eliminated by natural selection. I do not think that we can be expected to accept this unproved supposition as an argument for Darwinism.